CSHARP-1447: Allow serialization of generic IDictionary implementations with non-public constructors when serializing to an interface definition

Author: James Hadwen

src/MongoDB.Bson.Tests/Serialization/Serializers/DictionaryGenericSerializerTests.cs

@@ -14,7 +14,9 @@
 */
 
 using System;
+using System.Collections;
 using System.Collections.Generic;
+using System.Collections.ObjectModel;
 using System.IO;
 using System.Linq;
 using System.Text;
@@ -43,6 +45,19 @@ public class T
             public SortedList<object, object> SL { get; set; }
         }
 
+        public class RO<TKey, TValue> : ReadOnlyDictionary<TKey, TValue>
+        {
+            private RO(IDictionary<TKey, TValue> dictionary)
+                : base(dictionary)
+            {
+            }
+
+            public static RO<TKey, TValue> ConstructorReplacement(IDictionary<TKey, TValue> dictionary)
+            {
+                return new RO<TKey, TValue>(dictionary);
+            }
+        }
+
         [Test]
         public void TestNull()
         {
@@ -388,6 +403,28 @@ public void TestMixedPrimitiveTypesWithMixedKeys()
             Assert.Throws<BsonSerializationException>(() => obj.ToBson());
         }
 
+        [Test]
+        public void TestImmutablePrivateConstructorDictionaryImplementation()
+        {
+            var d = new Dictionary<object, object> { { "A", new C { P = "x" } } };
+            var id = RO<object, object>.ConstructorReplacement(d);
+            var sd = CreateSortedDictionary(d);
+            var sl = CreateSortedList(d);
+            var obj = new T { D = d, ID = id, SD = sd, SL = sl };
+            var json = obj.ToJson();
+            var rep = "{ 'A' : { '_t' : 'DictionaryGenericSerializers.C', 'P' : 'x' } }";
+            var expected = "{ 'D' : #R, 'ID' : #R, 'SD' : #R, 'SL' : #R }".Replace("#R", rep).Replace("'", "\"");
+            Assert.AreEqual(expected, json);
+
+            var bson = obj.ToBson();
+            var rehydrated = BsonSerializer.Deserialize<T>(bson);
+            Assert.IsInstanceOf<Dictionary<object, object>>(rehydrated.D);
+            Assert.IsInstanceOf<Dictionary<object, object>>(rehydrated.ID);
+            Assert.IsInstanceOf<SortedDictionary<object, object>>(rehydrated.SD);
+            Assert.IsInstanceOf<SortedList<object, object>>(rehydrated.SL);
+            Assert.IsTrue(bson.SequenceEqual(rehydrated.ToBson()));
+        }
+
         private SortedDictionary<object, object> CreateSortedDictionary(Dictionary<object, object> d)
         {
             var sd = new SortedDictionary<object, object>();

src/MongoDB.Bson/Serialization/Serializers/DictionaryInterfaceImplementerSerializer.cs

@@ -13,6 +13,7 @@
 * limitations under the License.
 */
 
+using System;
 using System.Collections;
 using System.Collections.Generic;
 using MongoDB.Bson.Serialization.Options;
@@ -164,7 +165,7 @@ public class DictionaryInterfaceImplementerSerializer<TDictionary, TKey, TValue>
         DictionarySerializerBase<TDictionary, TKey, TValue>,
         IChildSerializerConfigurable,
         IDictionaryRepresentationConfigurable<DictionaryInterfaceImplementerSerializer<TDictionary, TKey, TValue>>
-            where TDictionary : class, IDictionary<TKey, TValue>, new()
+            where TDictionary : class, IDictionary<TKey, TValue>
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="DictionaryInterfaceImplementerSerializer{TDictionary, TKey, TValue}"/> class.
@@ -271,7 +272,7 @@ public DictionaryInterfaceImplementerSerializer<TDictionary, TKey, TValue> WithV
         /// <returns>The instance.</returns>
         protected override TDictionary CreateInstance()
         {
-            return new TDictionary();
+            return Activator.CreateInstance<TDictionary>();
         }
 
         // explicit interface implementations